This invention generally relates to a flow rate transducer or detector which produces an electrical signal indicative of flow rate of fluid, such as fuel for internal combustion engine for vehicles, and more particularly, the present invention relates to a flow rate transducer of the type arranged to produce an intermittent signal by transmitting a light beam through a rotating member which rotates at a speed substantially the same as the fluid.
Generally speaking, in conventional flow rate transducers of the above-mentioned sort, an impeller or a blade wheel is rotatably mounted in a fluid chamber in such a manner that it rotates at a rotational speed substantially the same as the speed of fluid flow, and a light beam is arranged to pass through a given point of the locus of the blade wheel so that a pulsating signal will be produced since the light beam is intermittently received by a photosensitive element. Various conventional flow rate transducers of this sort can be divided into two types. Namely, in the first type, a light-emitting element, such as a light-emitting diode or a lamp, and a light-receiving element, such as a phototransistor, are both located at one side of the blade wheel, while a reflector is located at the other side to reflect the light beam from the light-emitting element. The light-emitting element and the light-receiving element as well as the reflector are isolated from fluid rotating the blade wheel, and suitable windows made of a transparent material for transmitting the light beam are provided in front of the light-emitting element and the light-receiving element and also in front of the reflector. In the second type, no reflector is used. Namely, a light-emitting element and a light-receiving element are respectively located at both sides of a blade wheel so that the light-receiving element directly receives the light beam from the light-emitting element. Similar windows are also provided in this second type.
The above-described conventional flow rate transducers have suffered hitherto a problem in connection with work for optical axes alignment. In both of the above-described conventional flow rate transducers, it is essential that the optical axes have to be aligned. In detail, in the first type, the position and the inclination angle of the light-emitting element have to be adjusted so that the light beam therefrom hits a predetermined position of the reflector; the inclination angle of the reflector has to be adjusted so that the light beam reflected thereat is properly transmitted to the light-receiving element, and the position and inclination angle of the light-receiving element have to be adjusted so that the optical axis thereof accords with the reflected light beam. Similarly, in the second type, the optical axes of the light-emitting element and the light-receiving element having to be aligned. Such optical axes alignment is essential for ensuring the light beam a correct propagation through the windows. However, this work for optical axes alignment has been troublesome and time-consuming hitherto because such adjustments for optical axes alignment had to be performed after the above-mentioned various elements have been incorporated in or assembled with the body or housing of the flow rate transducer.